linux-kernel - Re: [PATCH RESEND 3/5] KVM: X86: Boost vCPU which is in critical section

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Date:   Wed, 30 Mar 2022 00:07:01 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH RESEND 3/5] KVM: X86: Boost vCPU which is in critical
 section

On Fri, Mar 25, 2022, Wanpeng Li wrote:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 425fd7f38fa9..6b300496bbd0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10375,6 +10375,28 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
>  	return r;
>  }
>  
> +static int kvm_vcpu_non_preemptable(struct kvm_vcpu *vcpu)

s/preemtable/preemptible

And I'd recommend inverting the return, and also return a bool, i.e.

static bool kvm_vcpu_is_preemptible(struct kvm_vcpu *vcpu)

> +{
> +	int count;
> +
> +	if (!vcpu->arch.pv_pc.preempt_count_enabled)
> +		return 0;
> +
> +	if (!kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.pv_pc.preempt_count_cache,
> +	    &count, sizeof(int)))
> +		return (count & ~PREEMPT_NEED_RESCHED);

This cements PREEMPT_NEED_RESCHED into KVM's guest/host ABI.  I doubt the sched
folks will be happy with that.

> +
> +	return 0;
> +}
> +